I think this is related to threading but not the same thing. I seem to have lost the section at the top of the preview pane that tells you that a followup message was sent, or draft is present. How do I re-enable this?

That's odd, because I have always had it set up so that the sent mail goes to a special folder, and have always had the links to sent email at the top of the preview pane. Compressing it doesn't work. Other ideas? This is a really important feature for me.